Transition-metal-decorated 2D γ-graphyne as high-performance adsorbents for heavy metal removal: A DFT study toward descriptor-guided design.

Heavy metal (HM) toxicity has become one of the major environmental concerns in recent years. In this study, we investigate the adsorption-based approach for the detection and removal of heavy metal ions (HMIs) from wastewater applications. Density functional theory (DFT) calculations are used to systematically investigate pristine γ-graphyne (γ-GY) and transition-metal-decorated γ-graphyne (TM/γ-GY) as efficient adsorbents for Hg, As, and Pb removal under implicit solvation conditions. Pristine γ-GY exhibits adsorption of Hg, As, and Pb with adsorption energies of -1.17 eV, -2.21 eV, and -3.46 eV, respectively. Transition metal doping enhances adsorption performance via strengthened TM-C interactions, increased electron transfer, enhanced stability, and electronic structure tuning. Re/γ-GY and Os/γ-GY show exceptionally strong adsorption for As and Pb (-4.81 and -4.30 eV, respectively), while Mn/γ-GY offers balanced adsorption for all HMIs. TM doping reduces the γ-GY band gap from 0.37 eV to below 0.15 eV in several systems, enhancing both electrical conductivity and adsorption sensitivity. Sensitivity analysis shows that Re/γ-GY achieves ∼100% sensitivity toward As, while Mn/γ-GY and Os/γ-GY selectively respond to Hg with >90% sensitivity. Adsorption capacity calculations show that pristine γ-GY exhibits a Hg uptake of 1043 mg g-1, while TM doping enhances As and Pb capacities to 237 mg g-1 and 984 mg g-1 on Mn/γ-GY, respectively. Through a descriptor-guided framework incorporating adsorption selectivity, sensitivity, and adsorption capacity, Mn/γ-GY attains the highest overall performance score (0.72), making it the most promising adsorbent for multi-contaminant heavy metal removal.